This is globular cluster M53, one of the galaxy's densest star clusters. It packs thousands of stars into a space about 220 light-years across. It's hard even to imagine the eternally sparkling light show of a night sky you'd see inside M53.

Located some 58,000 light-years from Earth and 60,000 from the center of the Milky Way, M53 is one of the furthest outlying of the galaxy's globular clusters. The legendary astronomer William Herschel once described such clusters as "one of the most beautiful objects I remember to have seen in the heavens", and two centuries of improved telescopes have only served to confirm his assertion.

But M83 is unusual, even by the standards of the already remarkable globular clusters. NASA - which, incidentally, suggests its "night sky would glow like a jewel box of bright stars" - explains how this particular collection of stars is essential to solving the mystery of the blue straggler stars:

Most of the stars in M53 are older and redder than our Sun, but some enigmatic stars appear to be bluer and younger. These young stars might contradict the hypothesis that all the stars in M53 formed at nearly the same time. These unusual stars are known as blue stragglers and are unusually common in M53. After much debate, blue stragglers are now thought to be stars rejuvenated by fresh matter falling in from a binary star companion. By analyzing pictures of globular clusters like the above image taken by the Hubble Space Telescope, astronomers use the abundance of stars like blue stragglers to help determine the age of the globular cluster and hence a limit on the age of the universe.